Sometimes the best-intentioned efforts to fix a problem make it worse.

Or create another, even more serious problem.

And the results of the two biggest harness races of the weekend suggest that is what Harness Racing New Zealand may have done.

The industry's ruling body changed the rules governing eligibility for major 4-year-old races this season, opening them up to 5-year-olds as well.

It is easy to make an argument for the decision, as many 4-year-old features in recent years have struggled for numbers, and small fields are the enemy of turnover.

But Bettor Cover Lover destroying our best mares in the Queen Of Hearts at Alexandra Park on Friday and then Caribbean Blaster's come-from-last win in the Victoria Cup on Saturday will only increase fears that the HRNZ move is unfair.

Unfair to the owners of our best, and just below the best, 4-year-old pacers and trotters.

Because those horses may be losing their winning shot at six or seven races which their connections have every right to feel they could target.

Caribbean Blaster is a 5-year-old who has just won the toughest race in Australia.

That follows a trend where almost every serious race in New Zealand this season was won by 5-year-olds - Terror To Love in the NewZealand Cup, Gold Ace in the Free-For-All, Sushi Sushi in the Kaikoura Cup.

These horses now have megabuck goals like the Interdominion, Hunter Cup, Miracle Mile and Auckland Cup on their agendas and plenty of chances for group one glory andthe stud career benefits that go with it.

So why should they also get the chance to dominate their younger rivals in the Taylor Mile, Messenger Pace and Harness Jewels?

There are a couple of 4-year-olds good enough to stand up to their older rivals - Smolda and Fly Like An Eagle - but most will simply get blown away.

And that leaves them with very few winnable targets for the season.

Take exceptional 4-year-old Christian Me, who is unbeaten this season.

His trainer Cran Dalgety was aiming him at the Pelorus Classic in Blenheim next month until he found out Terror To Love is heading there.

Christian Me is good, but Terror To Love is a millionaire who has won two New Zealand Cups.

That is not a fair fight.

And the situation worsens at the season-ending Harness Jewels.

It is stakes-based, so the best 5-year-olds will all get a start.

What incentive does that give the trainers of all but the absolute best 4-year-olds to chase a Jewels spot or even keep racing that late in the season?

Taking on Bettor Cover Lover with a five-win, 4-year-old pacing mare. No thanks.

And the new rule could push more horses on to the export market.

The 4-year-old season is already a tough one, with horses losing their 3-year-old handicapping concessions so having to earn their stripes.

Now New Zealand harness racing basically has no 4-year-old races.

That has to increase the temptation to sell mid to high-class horses at the end of their 3-year-old careers, rather than having to throw them to the lions for greatly diminished returns next season.

So a move that was designed to increase the number of horses in the 4-year-old races might actually decrease the number of horses in the country, which is the last thing harness racing needs.

The rule change will undoubtedly provide some spectacular racing, with more star power and some of the best-known pacers in Australasia extending their seasons until the Jewels in June.

But it will really only further boost the bank balances of horses who already race for millions.

And give the owners of almost every good 4-year-old pacer or trotter in the country a viable reason to consider selling.